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SN65DP149: Replacement of TMDS171 with SNx5DP149

Naoki Maruyama
Prodigy 150 points
Part Number: SN65DP149
Other Parts Discussed in Thread: TMDS171

Hi team

I have a question.

We are currently designing an HDMI (1.4b) repeater board using the TMDS171.

However, due to availability issues, we are considering replacing it with the SNx5DP149 series.

Is it possible to use it by AC coupling the TMDS lanes and changing the surrounding circuitry?
I will rebuild the board specifically for this purpose.

Thank you.

maru

  • 0
    TI__Guru*** 149885 points

    Maru-san

    The DC-coupled HDMI source expects to see 3.3V common mode voltage which is normally provided by the TMDS171 RX, but now gets blocked by the AC coupling cap when switching to DP149. So in this case you would need to provide external 3.3V common mode voltage as shown below.

    Please note the external Rterm along with DP149 internal termination produces double termination and therefore will reduce the signal into DP149 input. A Rterm value of 50-Ω typically works with all HDMI TX, but also cuts in half the signal amplitude into DP149. If you are using 50-Ω, then you may need to increase the HDMI transmitter's voltage swing to compensate for the double termination. You can use a larger Rterm to minimize the impact of double termination, and the maximum value used for Rterm will depend on the HDMI TX capabilities.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 150 points

    Mr. David.

    Sorry for the delay in replying to you.
    I have understood.

    1) AC coupling is required.
    2) If AC coupling is used, the TX side also needs to be pulled up.
    3)If TX side is also pulled up, the drive capability of TX side must be high.
    4) The pull-up needs to be adjusted according to the drive capability.

    Thank you very much. I learned a lot.

    maru